Offshore gas treatment and/or CO2 capture units using amine wash processes comprise liquid or gaseous fluid absorption and regeneration columns. These columns operate under counter-current or co-current gas/liquid flow conditions and they are installed on vessels, floating barges or offshore platforms, of FPSO (Floating Production, Storage and Offloading) type or of FLNG (Floating Liquefied Natural Gas) type for example. Floating barges also comprise distillation columns or dehydration columns.
The columns used in these offshore gas treatment and/or CO2 capture and/or distillation and/or dehydration units are generally based on the principle of a material and/or heat exchange between the gas and the fluid that circulate in the columns. Contacting columns generally consist of a cylindrical enclosure provided with internal contacting elements promoting exchange between the fluids. The contacting elements (contactor) that increase the contact surface area can be structured packings, random packings or trays. FIG. 1 shows a particular case of a gas treatment column 1 equipped with a distributor tray at the column top. In this example, the gas (G) and the liquid (L) circulate in a counter-current flow. Conventionally, this gas treatment column 1 comprises several sections 3 filled by a contactor, and a distributor tray 2 is arranged above each contactor 3. The gas/liquid contactor contacts gas G with liquid L so as to allow exchanges.
The gas/liquid contact columns considered are placed on floating structures, of vessel, platform or barge type for example, sensitive to the wave motion. The equipments installed on these units, notably the gas/liquid distributor trays, therefore undergo wave motions up to six degrees of freedom (yaw, pitch, roll, heave, sway, thrust).
By way of indicative information, the angle associated with the combination of the pitch and roll oscillations is of the order of +/−5° with a period ranging from 10 to 20 s. The orders of magnitude of the longitudinal, transverse and vertical accelerations encountered in the column respectively range between 0.2/0.8/0.2 m/s2 6 m above the deck where the column is arranged and 0.3/1.3/0.3 ms2 50 m above the deck. Under such conditions, the operation of conventional contact columns can be greatly disturbed. Indeed, the effect of the wave motion can degrade the homogeneity of the phase distribution in the column section.
If it is not controlled, this poor distribution in the packing bed can substantially degrade the performances of the contact column. In order to avoid this type of problem, various suitable structured packing piles have been developed.
For example, patent application U.S. Pat. No. 5,486,318 discloses contactor embodiments with partitioning of the packing section. In a first embodiment, the packing section is partitioned by perforated walls. The column is thus made up of several compartments equipped with structured packings. In a second embodiment, each packing section is perpendicularly adjacent to the other section, thus the total section of the column is made up of a multiplicity of structured packing sections. However, for the embodiments described in this patent, the partitioning mode used can degrade the homogeneity of the flow in the column. Indeed, when a fraction of the liquid, under the effect of the sea motion, moves radially from one section to another, the liquid accumulates on the obstruction plane, which is, depending on the embodiment, a perforated wall or a packing plate. The accumulation of liquid coming from several packing sheets tends to form a preferred path for the liquid and the gas, thus degrading the transfer performances of the contact column.
Furthermore, patent application U.S. Pat. No. 5,984,282 discloses an embodiment of a contactor arrangement where the structured packing is arranged in a specific way so as to allow uniform distribution. However, this implementation is complex.
Besides, patent applications U.S. Pat. No. 7,559,539 and U.S. Pat. No. 7,559,540 disclose contactor embodiments where the packing bed consists of two structured packing types (geometric surface areas, angles, etc.). The packing beds having different areas can be superimposed in the axial direction of the column or in the radial direction according to the patent. In patent applications U.S. Pat. No. 7,559,539 and U.S. Pat. No. 7,559,540, the section of the column is not split into several packing sections, therefore, under the action of the three-dimensional wave motion, the embodiments do not allow to prevent lateral displacement of the liquid in all directions. These embodiments do therefore not provide good distribution of the liquid and vapour phases in an offshore environment.
In order to overcome these drawbacks, the invention relates to a contactor for a heat and/or material exchange column comprising an arrangement of two structured packings developing different geometric surface areas and having parallel principal directions. The present invention thus allows to ensure good homogeneity and uniformity of the distribution in the structured packing bed, therefore providing smooth operation of the column, notably in case of inclination thereof, whatever the direction of inclination of the column.